Although methods of producing footwear have long utilized machinery to help reduce labor costs, a large portion of the costs of producing footwear still is attributable to labor costs. In addition, to the extent footwear production has become mechanized, the economic advantages of mechanization are lessened when the machinery involved is under-utilized as, for example, by being idle for a significant portion of the footwear-making process. Thus, in general, the footwear production industry is hampered by processes which require a relatively large investment in labor and which do not provide for efficient utilization of machinery.
The problems of uneconomical methods of production are particularly acute in the sporting footwear industry, such as the hiking, skiing, and climbing footwear industries. This is because these types of footwear must combine durability, strength and comfort with the forms of resiliency and strength which are peculiarly required in the footwear intended for each type of sport. In the past, production of such footwear has required a number of steps such as stitching, nailing, gluing, all performed in a required sequence. The large number of steps required during actual construction of the footwear has required investment of a relatively large amount of labor time.
In general, these methods for the production of footwear, and particularly of sporting footwear, have begun with providing a number of pieces of substantially flat material including leather for the uppers, material for toe and heel counters, an insole, and an outersole.
According to the conventional methods of production, the piece forming the upper is joined along the back (heel) edges and a liner layer is attached to the inside of the upper by sewing at least along certain portions of the upper. Toe and heel counters are selected to match the size of the footwear being constructed. These toe and heel counters are placed between the liner and the upper and glue is applied. This assembly is then placed over a last which will act as a form for shaping the upper, liner and counters to the desired contours. The last is thus in the shape desired for the interior space of the footwear. An insole is attached to the bottom of the last. The upper, in conventional processes, is temporarily nailed or tacked to the last. The upper/liner/last assembly is placed in a lasting machine which applies pressure to stretch the upper over the last and form the upper, toe and heel counters and liner in the desired contours. The bottom edges of the upper, counters and liner are pulled around the bottom edges of the last and attached to the bottom surface of the insole by gluing, stitching, and/or nailing. In particular, it is common to glue and staple the upper, counters and liner to the bottom of the insole around its circumference, to additionally nail the heel portion of the upper to the bottom of the insole, and to sew the toe of the upper to the bottom of the insole. Such sewing produces stitches which extend through the insole, adversely affecting the waterproof qualities of the insole and also affecting the comfort of the wearer. After the gluing, sewing and nailing steps, the upper/insole/last assembly is heated, as by placing the assembly in an oven, in order to activate the heat-activated glue. After the glue attaching the bottom edge of the upper to the bottom of the insole has set, the staples are removed. The last is removed from the assembly and the lower surface of the assembly is subjected to grinding in order to even the surface and remove excess adhesive. Next, the bottom edge of the upper which has been glued to the insole is stitched to the insole using a machine especially designed for the purpose. In order to ensure an even surface for attachment of the sole, a filler material is applied to the bottom of the assembly. An adhesive is applied to the leveled lower surface of the assembly and this assembly and the sole are heated to activate the adhesives. The assembly and the sole are pressed together in a vise-type apparatus to ensure adhesion. At this point the assembly is essentially complete and the footwear is ready for final finishing and preparation for shipment.
As is apparent from the foregoing description, conventional methods for production of footwear are complicated, labor intensive, and require use of a number of specialized machines. Because the footwear is produced largely from unformed, flat, "raw" materials, a large amount of labor is required to bring the product to its final form. In addition, a number of specialized machines such as a lasting machine and a machine designed to sew the upper/liner to the insole are required. Since not all machine steps require the same amount of time, certain machines have a high proportion of idle time, further degrading the economics of footwear production.
Conventional methods of footwear construction also place constraints on the type of material which can be used. The multiple heating steps employed in conventional methods have a detrimental effect on many materials which could otherwise be used to provide thermal insulation or waterproof qualities to the footwear, such as certain types of plastics. The compression which occurs during treatment in a lasting machine is detrimental to insulating materials which depend on maintenance of a degree of loft for their insulating qualities. Materials which would otherwise provide waterproof qualities have those qualities compromised by a sewing step, often making necessary the provision of a sealant to accomplish waterproofing.
It is apparent, therefore, that several advantages could be obtained from the development of a process for production of footwear which yields the high quality particularly required for sports footwear but is less labor intensive and produces better utilization of machinery. In that regard, the present invention is directed to providing a process for producing footwear which efficiently utilizes both labor and machinery.